New materials, referred to herein as resistive memory materials, are now making it possible to produce non-volatile memory cells based on a change in resistance. Materials having a perovskite structure, among them colossal magnetoresistance (CMR) materials, are materials that have electrical resistance characteristics that can be changed by external influences.
For instance, the properties of materials having perovskite structures, especially CMR materials, can be modified by applying one or more short electrical pulses to a thin film or bulk material. The electric field strength or electric current density from the pulse, or pulses, is sufficient to switch the physical state of the materials so as to modify the properties of the material. The pulse is of low enough energy so as not to destroy, or significantly damage, the material. Multiple pulses may be applied to the material to produce incremental changes in properties of the material. One of the properties that can be changed is the resistance of the material. The change may be at least partially reversible using pulses of opposite polarity, or the same polarity but with wider width, from those used to induce the initial change.
Accordingly, a memory structure is provided, which comprises a substrate with a plurality of doped lines isolated from each other using shallow trench isolation, for example n-type bit lines isolated by oxide. Regions of the opposite dopant, for example p-type regions, are formed into the n-type bit lines to form diodes. Bottom electrodes overly the diodes. A layer of resistive memory material overlies the bottom electrodes. Top electrodes overly the resistive memory material. In a preferred embodiment, the top electrodes form a cross-point array with the doped lines, and the diodes are formed at each cross-point.
A method of manufacturing the memory structure is also provided. A substrate is provided and a doped-well, for example an n-well, is created. The doped-well is then divided into doped lines, for example n-type bit lines, by a shallow trench isolation process. The shallow trench isolation process simultaneous defines the doped lines, and isolates the doped lines from each other. Diodes are formed at what will become each cross-point of the cross-point array. The diodes are formed by doping a region of the doped lines to the opposite polarity, for example by implanting ions. Bottom electrodes are then formed over the diodes. A layer of resistive memory material is deposited over the bottom electrodes. Top electrodes are then deposited overlying the resistive memory material above the diodes such that a cross-point array is defined by the doped lines and the top electrodes, with a diode located at each cross-point. It may be possible, or even preferred, to achieve the method of manufacture in such a way the doped line, the diode formation, and the bottom electrode formation are all self aligned.